The present invention relates to a valve control system for an internal combustion engine, and more particularly, to such a system which can vary the operational characteristics of an engine poppet valve, in accordance with various operational modes of the engine.
Variable valve control systems for engine poppet valves are already generally well known in the art. Although such variable valve control systems can be applied to either the intake poppet valve, or the exhaust poppet valve, or both, it is most common to utilize such a variable valve control system to vary the “lift” (the amount of opening of the engine poppet valve) of only the intake poppet valves, and the invention will be described in connection with such an arrangement.
A “dual lift” valve control system is known from U.S. Pat. Nos. 4,762,096 and 5,660,153, both of which are assigned to the assignee of the present invention and incorporated herein by reference. In a typical dual lift valve control system, there is a low lift condition in which the poppet valve opens a relatively small amount while the engine is operating at relatively lower speeds, and a high lift condition in which the poppet valve opens a relatively large amount while the engine is operating at relatively higher speeds. Normally, such dual lift valve control systems require some sort of actuator (typically an electromagnetic or electro-hydraulic actuator) to move a latch member between unlatched (low lift) and latched (high lift) conditions. Although such dual lift valve control systems have shown the ability to perform in a generally satisfactory manner, there are many vehicle applications in which it is desirable to be able to select from among a greater range of lift options than merely “high” lift and “low” lift.
Also now well know to those skilled in the art are valve control systems of the type including “valve deactivation” capability. One embodiment of a valve deactivation control system is illustrated and described in U.S. Pat. No. 6,321,704, also assigned to the assignee of the present invention and incorporated herein by reference. In the valve deactivation system of the cited patent, there is an hydraulic lash adjuster (HLA) which may be operated in either: (i) a latched condition, in which case the rotation of the camshaft will result in normal valve lift, or (ii) an unlatched condition, introducing lost motion into the valve gear train, whereby rotation of the camshaft will result in very little lift, or more commonly, no lift at all of the engine poppet valve. Such valve deactivation systems have now started to enjoy a certain amount of commercial success, although the required latching mechanism, and the associated controls, add substantially to the cost of the engine valve train, especially considering that the result is merely a choice between normal lift and valve deactivation.
As is well know to those skilled in the art, in a typical dual lift valve control system, the dual lift capability would be provided for each and every cylinder. For example, on a V-8 engine, all eight of the intake poppet valves (assuming one intake valve per cylinder) would be provided with a dual lift valve control system, and normally, all of the intake poppet valves would operate “together”, i.e., all would be in the low lift mode or all would be in the high lift mode, at any given point in time.
On the other hand, on engines having valve deactivation capability (also referred to as “cylinder deactivation”), only a portion of the cylinders are deactivated. For example, on a V-8 engine, it would be typical to provide the intake poppet valves, and the exhaust poppet valves, for two of the cylinders on each bank with valve deactivation capability so that, as the engine speed and load reach predetermined values, all of the valves for those two cylinders of each bank would be deactivated, such that the engine then operates on four cylinders (i.e., as a “V-4” engine) at highway speeds and low throttle loads.
On certain vehicle engines, it would be desirable to provide both dual lift and valve deactivation capability. Unfortunately, based upon the known prior art, to provide even half of the engine poppet valves with both dual lift and valve deactivation capability would result in a valve control system which would be prohibitively expensive, and in many engine applications, would provide substantial packaging problems. The above disadvantage of the prior art is even more of a problem if, instead of “cylinder deactivation”, it is desired to provide true “valve deactivation”, and it will be understood that references hereinafter to “deactivation” will mean and include both cylinder-type and valve-type deactivation. In a true valve deactivation system, there would be two intake poppet valves per cylinder, and deactivation would be provided for one (typically, the “tumble” intake valve) of the two intake valves on each cylinder. Thus, the problems noted above regarding cost and packaging would be exacerbated by requiring deactivation capability on all eight cylinders.